Speaking solely about the Brexit debacle I also think Theresa May got the shitty stick.
I do think however she's not a negotiator, played a few things with regard to Brexit far too close to 'party' rather than 'country' - like getting other parties around the table much, much earlier in the process. But that's what advisers are for - to advise. I think she actually listened to the wrong people and tried to placate the wrong people.
I'm not sure if Boris (Gove, Rabb, Ledsom or whoever now puts themselves forward as leader of the Conservatives) will get a better deal. The EU are set on the backstop - MPs don't want it. If Boris etc can manage to the EU to back down on that or get MPs to vote for it they must be putting something in people's tea. So we'll go round in circles no matter who is PM from whatever party unless they can find an alternative to the back stop or do another referendum or walk away without a deal. I wouldn't want to be that person because they'll be in Theresa May's position very quickly.